Kunduz, Afghanistan (CNN) -- Police in the northern Afghanistan province of Kunduz are looking for a man they say strangled his wife after she bore him a third child that was not a son.
Sher Mohammed, 29, married his 22-year-old wife, Storay, four years ago, police said.
The couple had three daughters, the last of whom was born three months ago, said Khanabad district police chief Sufi Habib.
After the youngest daughter was born, Mohammed blamed his wife for not being able to deliver a boy, Habib said.
"Finally on Saturday, the man, with the help of his mother, first beat the woman and then strangled her to death," the police chief said.
Khanabad is about 50 kilometers (31 miles) from Kunduz city.
Police arrested the mother, Wali Hazrata, and detained her at the Kunduz city jail. But her son fled.
In a jailhouse interview, Hazrata said her son's wife committed suicide out of guilt.
"My son did not commit the crime," Hazrata said. "... But after three daughters, Storay herself felt guilty and committed suicide."
The report comes weeks after Afghan police said they rescued a 15-year-old girl who was locked up in the basement of her in-laws' house, starved, and had her nails pulled out.
The girl, Sahar Gul, was married off to a 30-year-old man last year. Authorities in northern Baghlan province said the girl reportedly was tortured after she refused to submit to prostitution.
Activists say women continue to suffer in parts of Afghanistan despite overall progress since the fall of the Taliban.
In the second quarter of last year, the Afghan Independent Human Rights Commission (AIHRC) registered 1,026 cases of violence against women. In 2010, it recorded 2,700 cases.
In December, gunmen attacked and sprayed an Afghan family with acid in their home after the father rejected a man's bid to marry his teenage daughter.
In another case, a 21-year-old, identified only as Gulnaz for her own protection, was sentenced to 12 years in prison after she reported that her cousin's husband had raped her.
Her plight attracted international attention when it came out that she had agreed to marry her attacker to gain her freedom and legitimize a daughter conceived in the attack. She was eventually freed, following President Hamid Karzai's intervention.
Horia Mosadiq, a London-based Afghan researcher for the rights group Amnesty International, said the abuse inflicted on Storay Mohammed is not an isolated instance.
"Generally the human rights situation, and particularly women's rights, is deteriorating," she told CNN. "I am in constant contact with women's rights groups across the country, and they say they are seeing an increase in violence."
This is in part because the Afghan government does little to implement or enforce the laws that protect women's rights, she said.
She also sees it as a consequence of women across the country gaining greater awareness of their rights, which is leading both to a backlash from men and to more cases of violence being reported.
On top of that, the Afghan government's move toward peace and reconciliation talks with the Taliban has led many people to think the current oppression of women will simply continue as it is, Mosadiq said.
"We need to make sure that we protect the women -- it's so important that women's rights in Afghanistan are non-negotiable," she said.
The alleged involvement of Storay Mohammed's mother-in-law in her abuse is not unusual, Mosadiq added, as women often play a role in violence against other women within the family, as do husbands, fathers and brothers.
And there is a heavy cultural pressure to bear sons, who are viewed as the breadwinners, she said, with the birth of a daughter seen as a burden rather than something to celebrate.
If the situation of Afghan women is to improve, Mosadiq said, a strong political will is needed at the government level, backed up by strong pressure from the international community.
"Where (the international community) puts so much pressure and focus on a military solution, they should also think about the protection of the Afghan people and Afghan women," she said.
CNN's Laura Smith-Spark contributed to this report.